[SI-LIST] Re: Algorithm to interpolate ramp data in IBIS
- From: Raghavendra Kulkarni <rkulkarn@xxxxxxxx>
- To: arpad.muranyi@xxxxxxxxx
- Date: Mon, 24 Nov 2003 18:15:53 -0800
Hello Arpad,
Please correct me if I'm wrong:
s2ibis2 evenly spaces the points for Rising/Falling waveforms. Also the end
points are decided by DC operating points generated through 50-ohm-Vcc and
50-ohm-gnd conditions. So that way these end points and intermediate time-steps
are fixed (total time/no of steps).
So the question is:
Is there a better way to generate these curves using s2ibis2? or should you
write a tool to iteratively interface with hspice to generate these curves?
Any feedback is appreciated!
Thanks!
-Raghavendra
Is there a way to inform
"Muranyi, Arpad" wrote:
> Nitin,
>
> You are absolutely correct, 100 evenly spaced points for
> the waveform tables (and also the IV tables) are not
> accurate enough in most cases.
>
> However, the IBIS specification does not describe how the
> point reduction should be done, nor does it specify how the
> tools should interpolate when reading such tables. On the
> other hand, the specification does say that the beginning
> and end of the waveform tables assume that the buffer is
> in steady state (i.e. they start and end with a 0 slope).
> It also says that the x-axis points do not have to be
> evenly spaced.
>
> As far as I know, most tools use only linear interpolation,
> but you need to ask your tool vendor how they do it on your
> own about these details.
>
> The tool I am using to make IBIS models does the following:
>
> 1) Extract the two end points, connect them with a virtual
> straight line and check where this "new curve" has the
> largest vertical distance from the original curve.
> 2) Pick up a new point at this largest distance, and connect
> the three points of this "new curve" with two straight
> lines, and check for the largest vertical distance again.
> 3) Loop this way until 100 points are picked up.
>
> I hope this helps.
>
> Arpad Muranyi
> Intel Corporation
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of BHAGWATH,NITIN
> (HP-Roseville,ex1)
> Sent: Thursday, November 20, 2003 3:55 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Algorithm to interpolate ramp data in IBIS
>
> Hello all,
>
> I am trying to convert a spice buffer model to ibis, and am having an =
> issue
> with the rampup/down portion. If I have a hundred (or fewer) points in =
> a
> rise or fall section with each point being sampled at a regular =
> interval,
> then the resolution of the curve seems to be inadequate for my purposes.
>
> I have been reading articles about selectively removing points in the =
> ramp
> up/down curves to reduce the number of points required for a given =
> accuracy.
> Unfortunately, I have been unable to definitevely find an algorithm used =
> by
> IBIS simulators to interpolate data points at timepoints not in the IBIS
> file given two data points in the IBIS file at timepoints on both sides =
> of
> the desired timepoint.
>
> My understanding so far is that to extrapolate any values at times =
> either
> before or after the endpoints of the curve, the last two points are =
> linearly
> extended. More critically (for getting a good algorithm for points
> removal), is it valid to assume that a voltage can be obtained for any
> arbitrary time by taking the voltages at the two closest timepoints, and
> linearly interpolating at the desired time using these two given points? =
> If
> so, then certain points can be removed if they can be obtained by two =
> more
> extreme points. Would there be any issues if the resulting ramp up/down
> curves no longer have points at regular intervals of time?
>
> Any help is much appreciated.
>
> Thanks
> -Nitin Bhagwath
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